Display a warning message when you try to send a song/album/artist that you've already sent to someone.
I share favorite tracks and new finds with a group of people quite often and I can never remember which songs I've sent to them already and which I haven't. I wouldn't want to spam their Spotify inbox with the same song that I've already sent them before, so a warning message would come in handy to let me know not to send it again!
This idea has been submitted more than 2 years ago but unfortunately hasn't gained enough kudos during that time (10 kudos/year). In order to keep an overview of the active ideas in this forum, this idea will be closed for now. Note that this does not mean the idea has been declined by Spotify.
Please feel free to re-post this idea if you still feel you want this implemented. With a little change in presentation, maybe this time it will gain the necessary support from the community.